U.S. patent number 6,369,710 [Application Number 09/534,851] was granted by the patent office on 2002-04-09 for wireless security system.
This patent grant is currently assigned to Lucent Technologies Inc.. Invention is credited to David Margin Poticny, R. Anthony Shober.
United States Patent |
6,369,710 |
Poticny , et al. |
April 9, 2002 |
Wireless security system
Abstract
A system provides a mobile transmitter and a plurality of
boundary tags for receiving communication from the mobile
transmitter. Preferably the mobile transmitter is coupled to a
mobile unit, which can be an inanimate object capable of moving or
being moved, or a living being. The boundary tags mark the
boundaries of an area within which the mobile unit is allowed to
move. The mobile transmitter transmits a signal to a boundary tag.
The system determines if the mobile transmitter has come into
proximity of a boundary tag by receiving a reflected modulated
signal from the boundary tag. If the mobile transmitter has come
into proximity of a boundary tag a response is generated. The
response can be a stimulus or an alert, or both. The response can
be generated at a central control station, or at a mobile
transceiver that includes the mobile transmitter and a mobile
receiver. In one embodiment, the boundary tag modulates a
reflection of the signal transmitted by the mobile transmitter.
This reflected modulated signal can be received by either the
mobile transmitter or by the central control station. In an
alternative embodiment invention, the boundary tag records the
receipt of the signal from the mobile transmitter. The central
control station transmits a second signal to the boundary tag. The
boundary tag modulates a reflection of the second signal to produce
the reflected modulated signal, which is then received at the
central control station. Optionally, the boundary tags may have
unique identifiers. The system could then include a processor
programmed to determine if the mobile transmitter is in proximity
of a boundary tag whose unique identifier matches one of the
predetermined unique identifiers. The processor can be located in
the central control station, or in the transceiver, or in another
location in the system.
Inventors: |
Poticny; David Margin (Chester,
NJ), Shober; R. Anthony (Red Bank, NJ) |
Assignee: |
Lucent Technologies Inc.
(Murray Hill, NJ)
|
Family
ID: |
24131789 |
Appl.
No.: |
09/534,851 |
Filed: |
March 27, 2000 |
Current U.S.
Class: |
340/572.1;
340/573.3; 340/573.4; 340/573.6 |
Current CPC
Class: |
G08B
13/1427 (20130101); G08B 13/2462 (20130101); G08B
21/023 (20130101); G08B 21/0247 (20130101); G08B
21/0261 (20130101); G08B 21/086 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G08B 13/14 (20060101); G08B
013/14 () |
Field of
Search: |
;340/573.4,573.3,573.6,572.1,5.92,10.1,505,539 |
References Cited
[Referenced By]
U.S. Patent Documents
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Other References
"A Microwave Noncontact Identification Transponder Using
Subharmonic Interrogation," Carol W. Pobanz, 8099 IEEE Transactions
on Microwave Theory and Techniques, 43 (1995), Jul., No. 7, PT. II,
New York, US, pp. 1673-1679. .
"A Coded Radar Reflector For Remote Identification Of Personnel And
Vehicles," Frank R. Williamson, Lacey F. Moore, Ralph Brooks, Julie
Anne Williamson, and Melvin C. McGee, Record of the 1993 IEEE
National Radar Conference, Lynnfield, MA, USA, Apr. 20-22, 1993,
ISBN 0-7803-0934-0, pp. 186-191..
|
Primary Examiner: Mullen; Thomas
Attorney, Agent or Firm: Lager; Irena
Parent Case Text
RELATED APPLICATIONS
Related subject matter is disclosed in the following applications
and assigned to the same Assignee hereof: U.S. Pat. Nos. 5,649,295,
5,649,296, 5,940,006, and 5,952,922.
Claims
What is claimed is:
1. A system comprising:
a mobile transmitter;
a plurality of boundary tags for receiving communications from the
mobile transmitter, at least one of the plurality of boundary tags
having a unique identifier; and
a mobile transceiver that comprises the mobile transmitter and a
mobile receiver; and
a central control station for communicating with the receiver, the
central control station comprising a processor programmed to
determine if the transmitter is communicating with at least one
boundary tag whose unique identifier matches at least one
predetermined unique identifier.
2. A system comprising:
a mobile transmitter;
a plurality of boundary tags for receiving communications from the
mobile transmitter, at least one of the plurality of boundary tags
has a unique identifier; and
a processor in communication with the transmitter, the processor
programmed to determine if the transmitter is communicating with at
least one boundary tag whose unique identifier matches at least one
predetermined unique identifier.
3. The system of claim 2, further comprising a mobile transceiver
that comprises the mobile transmitter and a mobile receiver.
4. The system of claim 3, further comprising a stimulus generator
responsive to the receiver.
5. The system of claim 3, further comprising an alert generator
responsive to the receiver.
6. The system of claim 3, further comprising a central control
station for communicating with the receiver.
7. The system of claim 6, wherein the central control station
further comprises an alert generator.
8. The system of claim 2, further comprising a central control
station for communicating with at least one of the plurality of
boundary tags.
9. A system comprising:
a mobile transmitter;
a plurality of boundary tags for receiving communications from the
mobile transmitter; and
a central control station for communicating with at least one of
the plurality of boundary tags, the central control station
comprises a receiver for receiving a reflected modulated signal
from the at least one of the plurality of boundary tags.
10. The system of claim 9, wherein:
at least one of the plurality of boundary tags has a unique
identifier; and
the central control station comprises a processor programmed to
determine if the mobile transmitter is communicating with at least
one boundary tag whose unique identifier matches at least one
predetermined unique identifier.
11. A system comprising:
a mobile transmitter;
a plurality of boundary tags for receiving communications from the
mobile transmitter; and
a central control station for communicating with at least one of
the plurality of boundary tags, the central control station
comprises a transceiver for transmitting a signal to the at least
one of the plurality of boundary tags and for receiving a reflected
modulated signal from the at least one of the plurality of boundary
tags.
12. A method of operating a security system having a plurality of
boundary tags and a central control station, the method comprising
the steps of:
transmitting a first signal from a mobile transmitter;
receiving the first signal using at least one boundary tag of the
plurality of boundary tags;
determining if the mobile transmitter has come into proximity of
the at least one boundary tag by receiving a reflected modulated
signal from the at least one boundary tag;
providing a response when the mobile transmitter comes into
proximity of the at least one boundary tag; and
receiving the reflected modulated signal at the central control
station.
13. A method of operating a security system having a plurality of
boundary tags and a central control station, the method comprising
the steps of:
transmitting a first signal from a mobile transmitter;
receiving the first signal using at least one boundary tag of the
plurality of boundary tags;
determining if the mobile transmitter has come into proximity of
the at least one boundary tag by receiving a reflected modulated
signal from the at least one boundary tag;
providing a response when the mobile transmitter comes into
proximity of the at least one boundary tag;
recording the receipt of the first signal at the at least one
boundary tag;
transmitting a second signal from the central control station to
the at least one boundary tag;
receiving the second signal at the at least one boundary tag;
and
receiving the reflected modulated signal at the central control
station.
14. The method of claim 13, wherein the step of determining if the
mobile transmitter has come into proximity of at least one boundary
tag comprises determining whether the at least one boundary tag
received the second signal.
15. A method of operating a security system having a plurality of
boundary tags and a central control station, and the method
comprising the steps of:
transmitting a first signal from a mobile transmitter;
receiving the first signal using at least one boundary tag of the
plurality of boundary tags at least one of the plurality of
boundary tags has a unique identifier;
determining if the mobile transmitter has come into proximity of
the at least one boundary tag by receiving a reflected modulated
signal from the at least one boundary tag, the reflected modulated
signal includes the unique identifier;
providing a response when the mobile transmitter comes into
proximity of the at least one boundary tag.
16. The method of claim 15,
further comprising the step of determining if the unique identifier
matches at least one predetermined unique identifier; and
the step of providing the response when the mobile transmitter
comes into proximity of the at least one boundary tag comprises
providing the response when the unique identifier matches at least
one predetermined unique identifier.
17. The method of claim 15, further comprising the step of
transmitting the unique identifier to a central control
station.
18. The method of claim 17,
further comprising the step of determining if the unique identifier
matches at least one predetermined unique identifier; and
wherein the step of providing the response when the mobile
transmitter comes into proximity of the at least one boundary tag
comprises providing the response when the unique identifier matches
at least one predetermined unique identifier.
Description
FIELD OF THE INVENTION
This invention relates to wireless communication systems and, more
particularly, to a wireless communication system used as a security
system.
BACKGROUND OF THE INVENTION
In some types of security systems it is desired to allow a mobile
unit to be able to move throughout a predetermined area in safety.
Such systems would generate an alert of some type when the mobile
unit moves out of the predetermined area. The mobile unit can be
any inanimate object, such as a motor vehicle or a container
capable of being transported, or the mobile unit can be any living
being, such as a pet or a human.
Some security systems utilize a centralized radio transmitter with
a radio receiver located on the mobile unit. When the mobile unit
strays out of range of the transmitter, the radio receiver assumes
the mobile unit has strayed out of the predetermined area and
provides some sort of feedback to the mobile unit. Additionally,
other systems have been developed (see U.S. Pat. Nos. 5,852,403 and
5,872,516) to track the movements of pets and provide feedback if
the pet strays from a predetermined area. One such system utilizes
a radio transmitter that sends a radio signal to a radio receiver
located on the pet. The radio receiver senses phase differences to
determine if the pet has strayed out of the predetermined area.
Another such system provides for a multiplicity of ultrasonic radio
transmitters, stationed around the periphery of the predetermined
area, which transmit to an ultrasonic receiver located on the pet.
Based on the presence or absence of the received ultrasonic signal,
the receiver determines if the pet has strayed from the
predetermined area and provides some sort of feedback to the pet.
Other pet security systems on the market today utilize lengths of
wire strung underground, the length of wire mark the periphery of
the predetermined area. A radio receiver located on the pet can
sense the presence of the underground wire and, in a similar manner
to the above, provide some sort of feedback if the pet has strayed
from the predetermined area.
There are various problems with each of the above systems. Systems
involving lengths of wire buried underground are expensive to
install and repair. These systems are also difficult to install if
a solid obstruction, for example a driveway, is in the way.
Furthermore, various "accidents" can cut the wires, thus rendering
the system non-functional. Additionally, the system could be
extremely difficult to repair since it may not be evident at what
specific location the wires are broken.
Systems that assume that the pet has left the predetermined area
when no longer in communication with the radio transmitter also
have deficiencies. First, the predetermined area may be of limited
size depending upon the maximum transmit power of the central radio
transmitter allowed under local or federal law. Second, radio
systems are notorious for being susceptible to variations in the
received signal strength of a radio signal from well-known
phenomena such as shadow fading, multipath fading, etc. Therefore,
simply because the pet's radio receiver does not receive radio
messages for a period of time does not mean that the pet has
strayed from the predetermined area. Third, such a system does not
easily allow for an irregularly shaped predetermined area. For
example, if the predetermined area has a swimming pool in the
middle, the pet owner may wish to allow the pet access to the
entire area with the exception of the pool area. A system that
utilizes a radio transmitter that sends a radio signal to a radio
receiver located on the pet could not cover this circumstance.
The system utilizing a multiplicity of ultrasonic radio
transmitters transmitting to an ultrasonic receiver located on the
pet is somewhat better in design, as it could to some degree handle
irregularly shaped predetermined areas. However, the presence of an
ultrasonic transmitter is costly both from the standpoint of
electrical power and the cost of each such transmitter.
Furthermore, the orientation of the receiver, such as whether the
receiver was in a line of sight orientation with the ultrasonic
transmitter or was shielded by the body of the pet, would tend to
make the specific dividing line between the predetermined area and
unsafe areas fuzzy and non-specific. The propagation
characteristics of such a transmitter are such that the incident
energy decreases as the square of the distance; a communications
technology in which the incident energy decreased more rapidly than
the square of the distance would tend to create a more clearly
defined dividing line. Thus, a fully deployed system utilizing the
ultrasonic technology for an extremely irregularly shaped
predetermined area could be costly, the dividing lines could be
difficult to predict, and such a system may also be difficult to
maintain due to the cost and/or complexity of equipment involved in
such a system. For example the cost of battery replacement in such
a system can be very costly.
Therefore, the objective of this invention is to develop a system
that does not suffer from the problems mentioned above.
Specifically, a system is needed that can handle predetermined
areas of arbitrary geometry with relatively clearly defined
dividing lines without drastically increasing the cost or the
complexity of installation or maintenance.
SUMMARY OF THE INVENTION
The invention solves the above and other problems by providing a
system that includes a mobile transmitter and a plurality of
boundary tags for receiving communication from the mobile
transmitter. The mobile transmitter can be part of a mobile
transceiver that also includes a mobile receiver. Preferably the
mobile transmitter is coupled to a mobile unit, which can be an
inanimate object capable of moving or being moved, or it can be
coupled to a living being. The placement of the boundary tags mark
the boundaries of a predetermined area, i.e., the area within which
the mobile unit is allowed to move.
The mobile transmitter transmits a signal to at least one boundary
tag. The system determines if the mobile transmitter has come into
proximity of the at least one boundary tag by receiving a reflected
modulated signal from the at least one boundary tag. If the mobile
transmitter has come into proximity of a boundary tag a response is
generated. The response can be a stimulus or an alert, or both. The
response can be generated at the transceiver, or at a central
control station.
In one embodiment of the invention, the at least one boundary tag
modulates a reflection of the signal transmitted by the mobile
transmitter. This reflected modulated signal is received by the
mobile transmitter. When the mobile receiver receives the reflected
modulated signal, it can either: determine if the mobile
transmitter has come into the proximity of a boundary tag; or it
can forward information obtained from the signal to a central
control station that would determine if the mobile transmitter has
come into the proximity of a boundary tag.
In an alternate embodiment of the invention, the at least one
boundary tag modulates a reflection of the signal transmitted by
the mobile transmitter, and this reflected modulated signal is
received by the central control station. Then, the central control
station would determine if the mobile transmitter has come into the
proximity of the boundary tag. In an additional alternative
embodiment of the invention, the boundary tag records the receipt
of the signal from the mobile transmitter. The central control
station then transmits a second signal to the boundary tag. The
boundary tag receives the second signal and modulates a reflection
of the second signal to produce the reflected modulated signal,
which is then received at the central control station.
Optionally, at least one boundary tag may have a unique identifier.
The system can then include a processor programmed to determine if
the mobile transmitter is in communication with at least one
boundary tag whose unique identifier matches at least one
predetermined unique identifier. This processor can be located in
the central control station, or in the transceiver, or in another
location in the system.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a block diagram of an illustrative Wireless Security
System;
FIG. 2 shows a particular embodiment of the illustrative Wireless
Security System of FIG. 1;
FIG. 3 shows a block diagram of an illustrative Transceiver used in
the Wireless Security System of FIG. 1;
FIG. 4 shows a block diagram of an illustrative Tag used in the
Wireless Security System of FIG. 1;
FIG. 5 shows a block diagram of an illustrative Central Control
Station used in the Wireless Security System of FIG. 1;
FIG. 6 shows a block diagram of an illustrative embodiment of the
Transceiver used in the Wireless Security System of FIG. 1 where
the Transceiver has two Integrated Circuits (ICs), a Digital IC and
a Radio IC;
FIG. 7 shows a block diagram of an illustrative Digital IC used in
the Transceiver of FIG. 6; and
FIG. 8 shows a block diagram of an illustrative Radio IC used in
the Transceiver of FIG. 6.
DETAILED DESCRIPTION
Overall Wireless Security System Operation
FIG. 1 shows a Transceiver 103 attached to a mobile unit,
therefore, making the Transceiver 103 a mobile transceiver. The
mobile unit can be any object capable of moving or being moved. For
example, the mobile unit can be an inanimate object, such as a
motor vehicle or a container capable of being transported. The
mobile unit can also be any living being, such as a pet or a human,
for example, a mentally infirm human or a human whose movements are
desired to be limited for any other reason.
Preferably, the Transceiver 103 includes a transmitter and a
receiver, i.e. a mobile transmitter and a mobile receiver, although
the Transceiver 103 can include just a transmitter.
The Transceiver 103 attached to the mobile unit communicates with a
multiplicity of Tags 105 using modulated backscatter, described
below. The Transceiver 103 further communicates with a Central
Control Station 101. The Central Control Station 101 can be any
processor, such as a controller, a microprocessor, or a base
station-processing unit. The Tags 105 are distributed around the
periphery of the predetermined area of safety, referred to herein
as a predetermined area, in such a manner that they define the
boundary of the predetermined area.
In addition to simply marking the external periphery of the
predetermined area, the Tags 105 can be located within the
predetermined area to "guard" specific areas that are unsafe, such
as a swimming pool. As shown in FIG. 2, Tags 105 can be placed in
an arbitrary manner to both surround the predetermined area
perimeter 220, and also to surround the Swimming Pool perimeter
240, thus making the predetermined area the area with the
predetermined area perimeter 220 excluding the swimming pool. This
concept can be extended to exclude additional areas that are
considered unsafe. Thus, the area of safety, i.e. the predetermined
area, can be of arbitrary geometry.
To obtain a sharp boundary line for the area of safety, several
things are needed. First, the effective range between the
Transceiver 103 and the Tags 105 should be relatively short; the
shorter the range, the more crisply the boundary line can be
established. Second, given the relatively short range, a number of
Tags 105 are required to define the boundary lines. Thus, it is
desirable for the Tags 105 to be relatively inexpensive. Modulated
backscatter meets both of these criteria. Modulated backscatter can
be used for communications between the Transceiver 103 and the Tags
105. As discussed below, the signal strength of a modulated
backscatter system decreases at least at the fourth power of the
distance between the Transceiver 103 and the Tags 105. Furthermore,
modulated backscatter has no active radio transmitter in the Tag
105 and thus the electrical components in the Tag 105 are not
costly; therefore the Tag 105 can be inexpensively manufactured and
a number of such Tags 105 can be deployed. It is preferable for the
Tags 105 to have their own electrical power. Thus, if a battery is
used to power the Tags 105, it is desirable to use a technology
that allows long battery life.
The Tags 105 could be deployed throughout the area of safety in a
number of ways. For example, the Tags 105 could be built into a
stake or marker and driven into the ground with the Tag 105 visible
at the surface. Alternately, the Tags 105 could be buried
underground at a relatively shallow depth. One advantage of
building the Tag 105 into a stake or marker would be that the Tags
105 could be located easily and re-positioned as required.
The Transceiver 103 regularly transmits a radio signal to the Tags
105 inviting any Tag 105 in range to respond using modulated
backscatter. The frequency of these radio transmissions is
calculated based upon the maximum speed of the mobile unit and the
effective range between the Transceiver 103 and the Tag 105. The
objective in determining a desirable frequency being to minimize
the likelihood that the Transceiver 103 would pass out of the
predetermined area without communicating with a Tag 105 that marks
the boundary of that area.
Modulated Backscatter Operation
The operation of a typical modulated backscatter system is now
described. FIG. 3 shows an overall block diagram of a Transceiver
103. The Transceiver 103 contains a Radio Signal Source 301 that
generates an RF Signal 302, typically a continuous wave (CW)
signal. The RF Signal 302 is sent to the Modulator 303. When a
Downlink Information Signal 305 is to be transmitted, then the
Modulator 303 modulates the Downlink Information Signal 305 onto
the RF Signal 302 using any one of a number of conventional
modulation techniques, such as Amplitude Modulation (AM), Phase
Modulation (PM), or Code Modulation (CM), to produce a modulated
signal. The modulated signal is then transmitted by the Transmitter
304, which sends this signal via Antenna 315 to a Tag 105. When a
Downlink Information Signal 305 is not present the RF signal 302
passes through the Modulator 303 and is transmitted by the
Transmitter 304 via Antenna 315.
In the Tag 105 (shown in FIG. 4), the Antenna 401 (frequently a
loop or patch antenna) receives an incoming signal. As described
above, this signal could be the modulated signal or the RF signal.
When there is Downlink Information Signal 305 modulated upon the
incoming signal, then the Downlink Information Signal 305 is
demodulated using the Detector/Modulator 402, which,
illustratively, could be a single Schottky diode. The result of the
Detector/Modulator 402 is a demodulation of the incoming signal
directly to baseband. The Downlink Information Signal 305 is then
amplified by Amplifier 403 and sent to the Processor 405. The
Processor 405 is typically an inexpensive 4 or 8 bit
microprocessor. In response to the incoming signal, the Tag 105
makes a determination if a response signal should be generated. If
a response is desired, then the Tag 105 generates an Uplink
Information Signal 406 to be sent from the Tag 105 back to the
Transceiver 103. To accomplish this, the Uplink Information Signal
406 is sent to a Modulator Control Circuit 407, which controls the
operation of the Detector/Modulator 402 by means of a Modulated
Signal 411. Thus, the Modulated Signal 411, containing the Uplink
Information Signal 406, is transmitted back to the Transceiver 103
using modulated backscatter. Alternately, the Modulator Control 407
could use the Uplink Information Signal 406 to modulate a
Subcarrier Signal 409 generated by the Frequency Source 408. The
Frequency Source 408 could be a crystal oscillator separate from
the Processor 405, or a signal derived from the output of a crystal
oscillator, or a frequency source derived from signals present
inside the Processor 405, such as a divisor of the fundamental
clock frequency of the Processor. The Modulated Signal 411, in this
embodiment is the result of modulating the Uplink Information
Signal 406 onto the Subcarrier Signal 409. The Modulated Signal 411
then is used by Detector/Modulator 402 to modulate the RF signal
received from Tag 105 to produce a modulated backscatter (i.e.,
reflected) signal. This may be accomplished by switching on and off
the Schottky diode of the Detector/Modulator 402 using the
Modulated Signal 411, thereby changing the reflectance of Antenna
401. A Battery 430 or other power supply such as a voltage circuit
420 (which can be a coil for example) provides power to the
circuitry of Tag 105. Although the use of a subcarrier is not
essential, it has been found that advantages are present to a
modulated backscatter design that uses a single frequency
subcarrier. Using such a subcarrier, many modulation schemes are
possible; e.g., Phase Shift Keying (PSK) of the subcarrier (e.g.,
BPSK, QPSK), or more complex modulation schemes (e.g., MSK, GMSK),
etc.
Returning to FIG. 3, the Transceiver 103 receives the modulated
backscatter signal with the Receive Antenna 310, amplifies the
signal with a Low Noise Amplifier 309, and demodulates the signal
using a Mixer 308. In some Transceiver designs, a single
transmit/receive antenna is used. In this event, an electronic
method of canceling the transmitted signal from that received
signal by the receiver chain is needed. This could be accomplished
by a device such as a circulator. In some designs, the Mixer 308 is
a Quadrature Mixer. Using the same RF Signal 302 in the Mixer 308
as is used in the transmit chain means the demodulation to baseband
is done using Homodyne detection; this has advantages in that it
reduces phase noise in the receiver circuits. The Mixer 308 then
sends the Demodulated Signal 311 (if a Quadrature Mixer, it would
send both I (in phase) and Q (quadrature) signals) to the Filter
Amplifier 307. The resulting filtered signal is then demodulated in
the Demodulator 306, which sends the recovered signal to the
Processor 300 to determine the content of the message and to
determine what actions to take.
Thus, in modulated backscatter, when the Transceiver 103 desires to
receive communications from the Tag 105, the Transceiver 103
typically generates a CW RF Signal 302 from the Radio Signal Source
301, which is sent in an unmodulated fashion through the Modulator
303 to the Transmitter 304 and transmitted by the Transmitter
Antenna 315. Thus, the signal received by the Antenna 401 of the
Tag 105 is an unmodulated CW signal. The Tag 105 then modulates a
Modulated Signal 411 onto the received unmodulated CW signal, which
is transmitted by the Antenna 401 back to the Transceiver 103.
Thus, the radio signal originally generated in the Radio Signal
Source 301 propagates from the Transceiver 103 to the Tag 105, and
is then reflected and re-transmitted from the Tag 105 back to the
Transceiver 103, thus encompassing two transmission paths.
One single transmission path in free space, with a line of sight
path between the two endpoints, propagates according to a square
law of propagation; i.e., the signal strength received at the
endpoint varies inversely with the square of the distance between
the endpoints. In modulated backscatter there are two transmission
paths, one path from the Transceiver 103 to the Tag 105, and the
other from the Tag 105 to the Transceiver 103. Therefore in
modulated backscatter the signal strength received back at the
originating endpoint varies inversely as the fourth power of the
distance between the endpoints. Indeed, if a line of sight path
between the endpoints does not exist, the signal strength could
vary inversely according to powers greater than four. Thus, in
modulated backscatter, the signal strength decreases rapidly with
increasing distance, making MBS an excellent candidate for a
wireless communications technology which has a relatively sharp
dividing line between areas in which communications are possible
and areas in which communications are not possible.
Using the above techniques as an example, an inexpensive,
short-range, bi-directional digital radio communications channel
using modulated backscatter is implemented. These techniques are
inexpensive as the components are (for example) a Schottky diode,
an amplifier to boost the signal strength, bit and frame
synchronization circuits, an inexpensive 4 or 8 bit microprocessor,
subcarrier generation circuits, and a battery or coil. Most of
these items are already manufactured in quantities of millions for
other applications, and thus are fairly inexpensive. Many of the
circuits mentioned above can be implemented in custom logic
surrounding the microprocessor core.
Maximizing Tag 105 Life
Once the Tags 105 are placed in their proper locations, as shown in
FIGS. 1 and 2, it is desirable for no further maintenance on the
Tags 105 to take place for a considerable length of time. This
means either that the Tags 105 are powered externally, or that the
Tags 105 are powered by a Battery 430 and designed in such a way to
maximize battery life. Several illustrative ways to maximize Tag
105 life are now discussed.
In one embodiment, the Tag 105 has no internal source of power. In
this event, one mechanism for obtaining electrical power is to
obtain power from the RF energy of the received RF signal. As seen
in FIG. 4 the output of the Detector/Modulator 402 is directed
towards a Voltage Circuit 420, which illustratively uses diodes in
a voltage doubling configuration to generate a voltage sufficient
to operate the electronics of the Tag 105. Although this embodiment
will operate properly, it relies on the incident RF energy for Tag
105 powering. Due to governmental restrictions governing the
emissions of RF radiation, it is likely that the Tag 105 would have
to be within a few feet of the Transceiver 103, and perhaps
considerably closer than a few feet, for there to be sufficient
incident RF energy to activate the Voltage Circuit 420 and generate
sufficient voltage for Tag 105 operation. This very short effective
range would likely require that Tags 105 be located very frequently
along the (for example) Predetermined area Perimeter 220, thus
increasing the cost of Tags 105 and the cost of installation of the
system.
In another embodiment, the Tag can be powered by a Battery 430. To
maximize the Battery 430 lifetime, a standard technique is to turn
off all or most of the electronic circuitry in Tag 105 for a period
of time, and then awaken the Tag 105 for a sufficient time interval
to allow the Tag 105 to determine if it is in the presence of a
Transceiver 103 that desires to communicate with the Tag 105. In
the Tag 105 design shown in FIG. 4, such a sleep and wakeup
function could be illustratively located in the Processor 405; many
commercial microprocessors have such sleep and wakeup capabilities
already implemented. When the Processor 405 enters a sleep mode, a
Power Management Control signal 413 is sent to a Power Management
Circuit 412 directing it to disconnect the Battery 430 from other
parts of the Tag 105, such as the Frequency Source 408, the
Modulator Control 407, and the Amplifier 403. Power would not be
disconnected from the Processor 405 to allow the Processor 405 to
re-awaken itself. Also, illustratively, the Power Management
Circuit 412 could implement a sleep and wakeup function independent
of the Processor 405. In this case, the Power Management Circuit
412 would disconnect the Battery 430 from all other parts of the
Tag 105. When the Tag 105 returns to the powered-on state, that is
once the Power Management Circuit 412 has powered on the Tag 105,
the Tag 105 then searches for a signal from the Transceiver 103
directing the Tag 105 to communicate using modulated backscatter.
An illustrative technique to detect the presence of a Transceiver
103 is discussed below. If no such Transceiver 103 is detected
after a certain period of time, then the Tag 105 can direct the
Processor 405 or the Power Management Circuitry 420 (as discussed
above) to re-enter sleep mode.
In still another embodiment, the Tag 105 does not cycle its power
on and off in a regular manner. Rather, the Tag's 105 normal
configuration is for the power from the Battery 430 to be
disconnected from the rest of the Tag 105 by the Power Management
Circuit 412. In this embodiment, the Voltage Circuit 420 is
enhanced to contain a circuit that has the capability to detect the
presence of incident RF energy received by the Antenna 401.
Illustratively, a Schottky diode used as a Detector/Modulator 402
can be designed as a "zero-bias detector." This means that the
Schottky diode can detect Amplitude Modulated signals transmitted
by the Transceiver 103 even if the Schottky diode is not currently
"biased" by a certain voltage. In this case, the only circuitry
required to be operational at all times is a relatively small
amplifier stage which amplifies these analog signals and compares
them to a fixed voltage level. If the fixed voltage level is
exceeded, then it is assumed that the Tag 105 is in the presence of
a Transceiver 103, and then the Power Management Circuit 412
activates the remainder of the Tag 105 by connecting the Battery
430 to the rest of the circuitry. The radio communications then
proceeds as described above for the other embodiments. The Tag 105
can then return to the "sleep"--i.e., unpowered--mode. For example,
the Tag 105 can return to the sleep mode after the Tag 105 has
transmitted a certain number of Uplink Information Signals 406.
Detailed Wireless Security System Operation
In one embodiment of the security system, the system simply alerts
the mobile unit when it comes near a Tag 105 marking the boundary
line between safe and unsafe areas, i.e. the boundary line of the
predetermined area. The Transceiver will, illustratively, transmit
an Downlink Information Signal 305 to the Tag 105 on a regular
basis. This Downlink Information Signal 305 could be a series of
Amplitude Modulated pulses of specific order or character. The
Detector/Modulator 402 of the Tag 105 demodulates these pulses,
transmits them to the Amplifier 403 which then transmits them to
the Processor 405. The Processor 405 determines if these pulses
conform to the predetermined pattern transmitted by the Transceiver
103. If yes, then the Processor 405 constructs an Uplink
Information Signal 406 which contains data indicating that a Tag
105 has detected the Downlink Information Signal 305 pulses sent by
a Transceiver 103. In this embodiment, the content of the Uplink
Information Signal 406 can be very simple. Illustratively, the
Uplink Information Signal 406 could be a single bit of
information--i.e., a "yes", indicating that this Tag 105 did in
fact detect the Downlink Information Signal 305--modulated by the
Modulator Control Circuit 407 onto a single frequency Subcarrier
Signal 409. The Demodulated Signal 311 received by the Transceiver
103 would then be an unmodulated signal at the frequency of the
Frequency Source 408. The Filter/Amplifier 307 and Demodulator 306
would then simply detect the presence or absence of this
unmodulated signal, most commonly by comparing the signal strength
at that frequency against a threshold signal strength. If the
Demodulator 306 determined that such an unmodulated signal is
present, then the Transceiver 103 would know that it was within
radio range of Tag 105, and the Transceiver 103 would provide some
type of stimulus to the mobile unit to which this Transceiver 103
is attached. This could be accomplished by the Processor 300
sending out a stimulus signal. Such a stimulus signal could
potentially be auditory (a musical note or tone, or a verbal
message), or perhaps electrical (a small electrical shock to the
pet), although the stimulus signal can be any kind of stimulus.
Alternatively, the Transceiver 103 can provide an alert either in
addition to or instead of the stimulus. Preferably the alert is be
given to whomever is responsible for the mobile unit. For example,
the alert can be delivered to a person responsible for the mobile
unit, or to a security system that would then cause the
predetermined area to be locked down. The alert can be auditory, or
electrical. In one embodiment, the alert is a phone call or page
that delivers a mess age to a person notifying the person that the
mobile unit has come close to a Tag. The alert can be provided by
alert generator 320.
In this embodiment, the Transceiver 103 does not need to know which
specific Tag 105 was the cause of the received unmodulated signal.
Indeed, it is possible that two or more Tags 105 were
simultaneously within radio range of the Transceiver 103, and all
of the Tags 105 within range could have contributed to the
reception of the unmodulated signal. Therefore, in this embodiment
there is no need for information as to the current location of the
Transceiver 103 (and thus of the mobile unit).
In an alternate embodiment, it is possible to enable the Tag 105
and the Transceiver 103 to determine with which Tag 105 the
Transceiver 103 is in communication. In this embodiment, the
Transceiver 103 begins with the transmission of a Downlink
Information Signal 305 that is similar to or identical to that
discussed in the above embodiment. The Tag 105 utilizes power
management techniques as discussed above. The Tag 105 further
detects the presence of the Downlink Information Signal 305 as
discussed above and informs the Processor 405, again as above. In
this embodiment, the Processor 405 generates an Uplink Information
Signal 406 that contains a piece of information unique to this Tag
105, including a unique electronic identifier. Thus, the Modulated
Signal 411 would include this unique identifier. The Transceiver
receives the Modulated Signal 411 and Filter/Amplifier 307 filters
the signal illustratively with a center frequency at the frequency
of the Frequency Source 408. The bandwidth of the filter is
designed to be greater than the occupied bandwidth of the Modulated
Signal 411. The Demodulator 306 then recovers the Uplink
Information Signal 406 from the received signal using conventional
demodulation techniques, the specific techniques depending upon the
type of modulation (BPSK, QPSK, etc.). In this embodiment, if more
than one Tag 105 is located within radio range of a Transceiver
103, then "collisions" between the Uplink Information Signals 406
from separate Tags 105 might occur, thus causing the Demodulator
306 to be unable to accurately demodulate a particular such Uplink
Information Signal 406. A number of techniques are known to solve
this problem, one illustratively being the technique called Aloha,
in which each Tag waits a random amount of time after receiving the
Downlink Information Signal 305 before transmitting the Uplink
Information Signal 406. Using these techniques, the Transceiver 103
can be informed of the unique identifiers of all Tags 105 in radio
range of the Transceiver. The Transceiver 103 can then apply a
stimulus to the mobile unit as discussed above.
In addition to, or instead of, the application of a stimulus, the
Central Control Station 101 can be informed of the unique
identifier of any Tag 105 that is in radio contact with the
Transceiver 103. For example, it is possible that particular Tags
105 have been pre-determined to be "extremely hazardous"--i.e.,
that if the Transceiver 103 comes into radio range of these
specific Tags 105, then an alert should be given, preferably the
alert should be given to whomever is responsible for the mobile
unit. To accomplish this, the Transceiver 103 could generate a more
complex Downlink Information Signal 305 which includes the unique
identification numbers of any Tag 105 with which the Transceiver
103 comes into communication. This more complex Downlink
Information Signal 305, including the Tag 105 unique identification
numbers, is then modulated in the Modulator 303, transmitted by the
Transmitter 304, and received by the Central Control Station 101.
FIG. 5 shows an illustrative Central Control Station 101. The
Central Control Station 101 illustratively includes a Low Noise
Amplifier 502, a Mixer 503 and Frequency Source 504 to demodulate
the incoming RF signal to baseband, a Filter/Amplifier 505 to
filter and amplify the received signal, and a Demodulator 506 to
recover the complex Downlink Information Signal 305. It is not
necessary for the modulation technique used for communications
between the Transceiver 103 and the Central Control Station 101, to
be the same modulation technique as used between the Transceiver
103 and the Tags 105. Indeed, it is most likely that the
Transceiver 103 to Tag 105 modulation scheme will be relatively
simple, such as Amplitude Shift Keying, for reasons discussed
above. For Transceiver 103 to Central Control Station 105
communications, any number of modulation techniques could be used,
such as Phase Shift Keying or Spread Spectrum techniques.
Once the Downlink Information Signal 305 is recovered by the
Central Control Station 101, the information contained within the
Downlink Information Signal 305 can be processed by the Processor
507 and stored in a Tag ID Database 509. The Tag ID Database would
then contain a record of those Tags 105 that came into range of the
Transceiver. Alternatively, only information pertaining to those
Tags 105 that are considered to be "dangerous" could be stored in
the Tag ID Database 509. The Tags can store whether they are
considered dangerous, or the Tag ID Database 509 could contain the
identity of the Tags considered dangerous. In the later case, the
Processor can compare the identity of the Tags with the information
store in the Tag ID Database 509 to determine if the Tag is
considered dangerous. If the Processor 507 detects that the
Transceiver 103 has come close to a dangerous Tag 105, then the
Processor 507 could generate and direct an alert signal 508
notifying that the Transceiver 103 has come close to a dangerous
Tag. For example, the Processor 507 could direct the alert signal
508 to be delivered to a person responsible for the mobile unit, or
the Processor 507 could direct the alert signal 508 to be delivered
to a security system that would then cause the predetermined area
to be locked down. The alert signal 508 could be auditory, or
electrical. In one embodiment, the alert is a phone call or page
that delivers a message to a person notifying the person that the
mobile unit has come close to a dangerous Tag. Either or both the
stimulus and the alert can be generated either when the Transceiver
103 comes into range of a Tag 105, that is considered dangerous, or
when the Transceiver 103 comes into contact with any of the Tags
105.
Note that there is a considerable difference in the effective range
between the Transceiver 103 and the Tags 105, and between the
Transceiver 103 and the Central Control Station 101. The range
between the Transceiver 103 and the Tags 105 is very short, in part
because the Detector/Modulator 402 is a very inefficient signal
detector. However, the Central Control Station 101 can have a much
more sophisticated radio receiver which could successfully receive
signals at a much greater distance even with the same transmit
power output from the Transmitter 304.
Transceiver 103 Design
Since the Transceiver 103 is attached to the mobile unit, it is
important that the Transceiver 103 not be excessively large, heavy,
or require excessive amounts of electric power. Until recently,
radio designs such as the Transceiver 103 illustratively shown in
FIG. 3 have been relatively large, since in many cases each
component shown in FIG. 3 is separately designed and
fabricated.
It is possible to consider the design of a Transceiver 103 which
would follow the block diagram of a Transceiver 103, as shown in
FIG. 3, but which would utilize a minimum number of electronic
integrated circuits. In one example, FIG. 6 shows a Transceiver
design that has two Integrated Circuits (ICs). In this design the
functions of the Transceiver 103 are separated into two IC's; a
Digital IC 610 and a Radio IC 620.
FIG. 7 shows a block diagram of the Digital IC 610, which includes
the Processor 300 and the Demodulator 306. The functions of the
Filter/Amplifier 307 have been divided into that of a Filter 710
and a Subcarrier Amplifier 810 (shown in FIG. 8). The Transceiver
is divided into the Digital IC 610 and a Radio IC to separate out
those functions which could be performed digitally in a CMOS IC, or
those functions which do not require high frequency (i.e. RF)
signal response. The functions being performed in the Filter 710
and the Demodulator 306 could be programmed as digital processes
into the Processor 300; alternatively, those functions could be
implemented in custom logic surrounding the Processor 300 core on
an IC.
The functions of the Radio IC 620 are illustratively shown in FIG.
8. The input to the Radio IC 620 is the Downlink Information Signal
305, and the output from the Radio IC 620 is the Amplified
Subcarrier 630. The Radio IC 620 also has connections to the
Transmitter Antenna 315 and to the Receive Antenna 310. As
discussed above, other embodiments of modulated backscatter could
utilize a single Transmit/Receive Antenna. In the Radio IC 620, the
Radio Signal Source 301 generates an RF Signal 302, which is then
modulated by the Downlink Information Signal 105 in the Modulator
303. This modulated RF signal is then transmitted by the
Transmitter 304. The reflected modulated signal received from the
Tag 105 is then received by the Receive Antenna 310 and amplified
by the Low Noise Amplifier 309 which operates at the RF frequency.
The amplified signal is then demodulated, illustratively here using
Homodyne detection, in the Mixer 308. The output of the Mixer 308
is then amplified by the Subcarrier Amplifier 810 whose circuits
must operate not at RF frequencies but at the frequency of the
Frequency Source 408 which generates the Subcarrier Signal 409.
Subcarrier frequencies are generally much less than RF frequencies;
generally Subcarrier of frequencies below a few Megahertz are
utilized. All of these components operate at either RF frequencies,
which could be as high as several Giga Hertz, or at frequencies up
to a few Megahertz. These functions can be implemented in an IC
process designed for high frequency operation, such as a Bipolar
silicon processor, or a Gallium Arsenide process.
One of the major causes of current consumption and heat dissipation
in the Transceiver 103 is the Transmitter 304. For some modulated
backscatter applications, transmit powers of one Watt or more are
utilized, in order to maximize the effective system range between
the Transceiver 103 and the Tag 105. However, for this application,
the goal is not to maximize system range, but rather to design the
system to support a range large enough such that an excessive
number of Tags 105 are not required. Typically, the output power of
the Transmitter 304 could be reduced to under 50 Milli Watts (+17
dBm) and still maintain a range from Transceiver 103 to Tag 105 of
approximately 15 feet. Thus, Tags 105 could be placed every 20-30
feet along the perimeter of the predetermined area. This transmit
power could be supported within a high frequency IC. If power
dissipation problems exist, a separate power amplifier IC could be
designed and placed inside a Multi-Chip Module, together with
another IC to perform the other functions of FIG. 8, the Multi-chip
Module would then comprise the Radio IC 620.
The foregoing is merely illustrative. Thus, for example, in the
illustrative embodiment the RF signal is transmitted from the
Transceiver 103 to at least one of the Tags 105. The Tag 105
backscatter modulates a reflection of the RF signal to produce a
reflected modulated signal. The reflected modulated signal is then
received at the Transceiver 103. In one alternative embodiment of
the invention, the reflected modulated signal can be received at
the central control station 101 instead of at the Transceiver. To
facilitate the reception of this signal, the central control
station should have as close a copy of the RF Signal 302 as
possible. It may be possible for the central control station 101 to
"listen" for the RF Signal 302, and using frequency and phase
locking techniques, reconstruct a signal as close as possible to RF
Signal 302 for use in demodulating the reflected modulated
signal.
Additionally, in another alternative embodiment of the invention,
instead of backscatter modulating a reflection of the RF signal to
produce a reflected modulated signal, the Tag 105 records the
receipt of the RF signal. The central control station 101 then
transmits a second RF signal to the Tag 105. The Tag receives the
second signal and backscatter modulates a reflection of the second
RF signal to produce the reflected modulated signal. The reflected
modulated signal is then received at the central control station.
In this embodiment, the central control station contains
transmitter and receiver circuitry which could be similar to that
shown in FIG. 3, with the possible exception that the RF power from
the Transmitter 304 may be greater than that used by the
Transceiver 103, since the range from the central control station
101 to the Tag 105 is greater than the range from the Transceiver
103 to the Tag 105.
While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art having reference to the specification and drawings that various
modifications and alternatives are possible therein without
departing from the spirit and scope of the invention.
* * * * *